Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming, and ultimately very expensive endeavors. As a result, over the years, a significant amount of added emphasis has been placed on well monitoring and maintenance. Once more, perhaps even more emphasis has been directed at initial well architecture and design. All in all, careful attention to design, monitoring and maintenance may help maximize production and extend well life. Thus, a substantial return on the investment in the completed well may be better ensured.
In the case of well monitoring and logging, mostly minimally-invasive applications may be utilized which provide temperature, pressure and other production related information. By contrast, well design, completion and subsequent maintenance, may involve a host of more direct interventional applications. For example, perforations may be induced in the wall of the well, debris or tools and equipment removed, etc. In some cases, the well may even be designed or modified such that entire downhole regions are isolated or closed off from production. Such is often the case where an otherwise productive well region is prone to produce water or other undesirable fluid that tends to hamper hydrocarbon recovery.
Closing off well regions as noted above is generally achieved by way of setting one or more inflatable packers. Such packers may be set at downhole locations and serve to seal off certain downhole regions from other productive regions. Delivering, deploying and setting packers for isolation may be achieved by way of coiled tubing, or other conventional line delivery application. The application may be directed from the oilfield surface and involve a significant amount of manpower and equipment. Indeed, the application may be fairly sophisticated, given the amount of precision involved in packer positioning and inflation. Proper packer inflation, in particular may be quite challenging, given the high and variable temperature and pressure extremes often present downhole which can affect fluid inflation.
In order to avoid the significant challenges associated with setting packers via inflation, packers may be configured for setting via swelling. That is, rather than equipped with an internal bladder for inflation, a packer may be more monolithic in nature and of a material configured to swell upon exposure to certain downhole conditions. Often, the packers may be of material configured to expand or ‘swell’ upon exposure to water-based fluid such as water, brine or other saline containing water. So, for example, an un-deployed swell packer may be positioned at a downhole location for isolation as alluded to above. Thereafter, usually over the course of between a few hours and a few days, the swell packer may swell and set into a sealing engagement with the well at the noted downhole location. Generally, by the time the packer is fully set, a profile is attained that is two to three times that of the packer in its original un-deployed state.
The above described packer, like other swellable devices, takes the form of a swellable fixture in the well. That is, as opposed to briefly introduced interventional tool, a packer is generally employed on a long-term basis. Even where the packer is utilized for temporary isolation, it is unlikely that the packer would be employed for less than a week. Once more, it is much more likely that the packer is set in place to maintain an isolation for the life of the well, which is often greater than 20 years in duration. Unfortunately, the reliability of the swell packer in terms of remaining adequately set over the long-term is less than desirable. Indeed, due to fluctuations in brine or salt concentration of the water-based fluid, the performance of the swell packer may also be quite variable as described below.
Swell packers as described above are generally of elastomers specially configured to swell in the presence of brine. As used herein, the term brine is meant to refer to any water-based fluid containing a measurable concentration of a salt such as sodium chloride. Unfortunately, the swelling character of the elastomers employed is variable in relationship to the variability in salt concentration of the brine. That is, as the salt concentration increases, so to does the amount of swell. So, for example, as concentration moves from 1% to 5%, the expansion ratio of the swell packer may dramatically increase (e.g. generally by more than about 75% in overall attained profile).
In order to address performance variability in the swell packer, extra effort may be placed on profiling and/or estimating downhole salt concentration in combination with careful selection of packer dimension and elastomer choice. However, such efforts fail to account for the long-term nature of the packer deployment. That is, with a likely deployment of between a week and up to twenty years or more, the odds of significant changes in downhole salt concentration are nearly guaranteed. As a result, the risk of packer failure due to shrinkage or over expansion and degradation is almost just as likely. Indeed, at present, follow-on costly interventional applications, such as cementing or additional packer deployments, are often required to remedy swell packer failure in downhole well locations of volatile salt concentrations.